Methods and apparatus for inspecting tubular goods using a continuous signal calibrating system

ABSTRACT

In the new and improved radiation apparatus disclosed herein for inspecting tubular goods, a radiation detector is coaxially positioned within a tubular member being axially translated along a selected inspection axis for receiving radiation from a radiation emitter facing the detector and rotating around the exterior of the tubular member. In the preferred embodiment disclosed herein, a unique radiation-attenuating device or shutter is cooperatively arranged to be normally interposed between the radiation emitter and the radiation detector to at least reduce the intensity of radiation imposed on the detector when a tubular member is not being inspected. The shutter is moved by selectively-operated controls to a second position as a tubular member that is to be inspected is placed between the radiation emitter and detector. In practicing the methods of the present invention with the disclosed apparatus, the shutter is uniquely arranged to cooperate with the detector circuitry for developing a comparison signal when the shutter is interposed between the radiation emitter and detector. The accuracy of this comparison signal is further assured by providing one or more clamping devices which are uniquely arranged for securing the radiation detector in a selected position when the comparison signal is developed.

United States Patent Tompkins 1 Aug. 8, 1972 [54] METHODS AND APPARATUSFOR INSPECTING TUBULAR GOODS USING [57] ABSTRACT A CONTINUOUS SIGNAL Inthe new and improved radiation apparatus disclosed CALIBRATING SYSTEMherein for inspecting tubular goods, a radiation detec- [72] Inventor:David R. Tompkins, Houston, Tex. tor is coaxially positioned within atubular member being axially translated alon a selected ins ection [73]Asslgnee' Corpon' axis for receiving radiation ffom a radiation emittercw or facing the detector and rotating around the exterior of [22]Filed: March 26, 1970 the tubular member. In the preferred embodimentdis- [21] AppL No: 22,935 closed herein, a unique radiation-attenuatingdevice or shutter IS cooperatively arranged to be normally Interposedbetween the radiation emitter and the radiation 250/833 D, 250/83detector to at least reduce the intensity of radiation 250/106 S imposedon the detector when a tubular member is Int- Cl- ..Golt not beinginspected The hutter is moved elec- [58] Field of search-"250,83 106tively-operated controls to a second position as a tu- 250/52 bularmember that is to be inspected is placed between the radiation emitterand. detector. In practic- [56] References C'ted ing the methods of thepresent invention with the dis- UNITED STATES PATENTS closed apparatus,the shutter is uniquely arranged to cooperate with the detectorcircuitry for developing a 2,829,268 4/195 ChOPe C UX comparison signalwhen the shutter is interposed 2,549,402 4/1951 Vossbefg, Jr C UXbetween the radiation emitter and detector. The accu- 2,964,630 12/1960Bosch ..250/83.3 D X racy of this comparison signal is further assuredby providing one or more clamping devices which are uniquely arrangedfor securing the radiation detector in a selected position when thecomparison signal is developed.

14 Claims, 9 Drawing Figures PNENTEDAUR M2 3.6811187 SHEEI 2 0F 4 Q2David R. Tompkins INVENTOR 1 FIG. 4 izj g g ATTORNEY PATENTEDMIB sum 93.693.187

' SHEET 3 BF 4 FIG. 5A

DETECTOR 25 FIG. 5 B

90 DETECTOR 2 2 e +(e -e 25 ADD 7 2 A00 M l *0 91-92 e l Iii-e -e FIG.5G I I 90 DETECTOR ?3 1 3 FIG. v

4 9 4 DETECTOR e, +(e -e T 25 ADD 0 4 David R, Tompkins 92 INVENTORATTORNEY David R. Tompkins INVENTOR ATTORNEY METHODS AND APPARATUS FORINSPECTING TUBULAR GOODS USING A CONTINUOUS SIGNAL CALIBRATING SYSTEMElongated tubular goods, such as oil-field piping or tubing and thelike, are frequently inspected for hidden flaws and other latent defectsthat might cause failure of such tubular members while in service. Asone aspect of such inspections, it is often desired to also obtainrepresentative measurements of wall thickness of such tubular members atspaced points along their length. It will be recognized, of course, thatsuch thickness measurements must be obtained at several points aroundthe circumference of a pipe as well as along its entire length to becertain of reliably detecting imperfections.

Various thickness-measuring devices have, of course, been devisedheretofore for inspecting long lengths of pipe and tubing. For instance,one typical device of this nature employs a rigidly-interconnectedradiation detector and radioactive source that are simultaneouslyrotated around an axially-moving pipe, with the resulting variations inmeasured radiation intensity being used to derive correspondingwallthickness measurements along a generally-helical path around thetubular member. Although the ideal situation would be to move the pipebeing inspected slowly and rotate the radiation devices at high speeds,practical considerations necessarily restrict these units to lowrotative speeds which correspondingly further limit the axial speed ofthe pipe joints and, therefore, result in inefficient inspection rates.

Alternatively, the new and improved inspection device disclosed in acopending patent application (Ser. No. 744,861) by the present inventorhas been found to provide accurate thickness measurements of varioustubular goods at efficient inspection rates. As described in thatapplication, a radiation detector is mounted on the free end of a fixed,but relatively flexible, elongated lance that is aligned along aselected inspection axis and adapted to receive a tubular member beingmoved axially along the axis. A radiation source is suitably mountedwithin an annular rotatable member adapted for rotation at high speedsaround the exterior of a tubular member moving along the inspectionaxis. By means of a unique arrangement of converging focusing slots, asharply-defined radiation pattern substantially smaller in area than theactive portion of the radiation detector is imposed thereon. In thismanner, limited lateral or vertical movements of the radiation detectorconfined within the moving tubular member being inspected will produceonly a negligible effect on the measurements provided by the radiationdetector.

Although this new and improved inspection apparatus has proven to besuccessful in certain situations, it has been found that where typicaloil-field tubular goods are being inspected, the efficiency of thisapparatus is significantly improved where the radiation means usedtherewith produce a substantial count rate at the detector in the orderof to counts per second as a tubular member is being inspected. Withcount rates of this magnitude, it will be appreciated that the detectorwill be operated at optimum statistical accuracy so that pipes can bemoved through the inspection apparatus at reasonably-high axial speedswithout unduly compromising the accuracy of the resulting thicknessmeasurements.

To produce such high count rates while there is an intervening pipe wallbetween the radiation means and detector will, of course, cause thedetector to be subjected to much-greater count rates when a pipe is notpositioned over the detector. It has been found, however, that with eventhe highest-quality radioactivity detectors, the prolonged exposure ofthe detector to such greatly-increased count rates will rapidly causethe detector to begin drifting and that this drift or error isaccelerated at an exponentially-increasing rate so long as the exposureis continued. Moreover, it has been found that even brief directexposures of even a high-quality radioactivity detector to suchgreatly-in creased count rates will quickly initiate unreliable orunstable operation of the detector which will not be corrected until thedetector has been inserted into a pipe for a considerable period oftime. Such unpredictable operation of the detector will, of course,either result in unreliable measurements being obtained or make itnecessary to delay the. inspection of another pipe until the detectorhas again stabilized.

Accordingly, it is an object of the present invention to provide new andimproved methods and apparatus for accurately measuring the wallthicknesses of elongated tubular members such as oil-field tubulargoods.

It is a further object of the invention to provide new and improvedradiation apparatus for inspecting axially-moving tubular members inwhich the operation of the radiation detector employed therewith isselectively stabilized for providing more-accurate measurements.

It is still another object of the present invention to provide new andimproved methods and apparatus for calibrating the radiation detectoremployed with a radiation inspection system to obtain more-accuratemeasurements. I

These and other objects of the present invention are attained byarranging radiation-emitting means to be rotated around a tubular membermoving axially along a selected axis for laterally directing radiationthrough at least one wall of such a member and towardradiation-detecting means spatially disposed from the radiation-emittingmeans and operatively associated therewith. Selectively-operableradiation-controlling means are movably positioned between theradiationemitting means and the radiation-detecting means and arrangedfor permitting the radiation-detecting means to be subjected to the fullintensity of the radiation emitting means only when a tubular member isinterposed between the radiation means. Upon removal of a tubular memberfrom the inspection apparatus, the radiation-controlling means are movedto another position for reducing the intensity of radiation imposed onthe radiation-detecting means to a selected level. By arranging theradiation-controlling means to reduce the radiation intensity forproducing a signal of known magnitude from the detecting means when atubular member is removed from the apparatus, the radiationdetectingmeans can be accurately calibrated. in practicing the methods of thepresent invention, these objects are attained by obtaining a firstsignal representative of a known thickness, obtaining one or more secondsignals representative of unknown thicknesses and then comparing thefirst and second signals to determine these unknown thicknesses.

The novel features of the present invention are set forth withparticularity in the appended claims. The invention, together withfurther objects and advantages thereof, may be best understood by way ofthe following description of exemplary methods and apparatus employingthe principles of the invention as illustrated in the accompanyingdrawings, in which:

FIG. 1 schematically illustrates thickness-measuring apparatus employingthe radiation-controlling means of the present invention as it may bearranged for cooperation with typical flaw-inspection apparatus;

FIG. 2 is an elevational view, partially in cross-section, of apreferred arrangement of the thickness-measuring apparatus depicted inFIG. 1;

FIG. 3 is an enlarged cross-sectional view taken along the lines 33 inFIG. 2 and depicts a preferred embodiment of radiation-controlling meansarranged in accordance with the principles of the present invention;

FIG. 4 is a schematic block diagram of a preferred embodiment of the newand improved calibrating circuitry of the present invention;

FIGS. 5A-5D respectively depict the successive operations of thecircuitry shown in FIG. 4 during the performance of the new and improvedmethods of the present invention; and

FIG. 6 is a cross-sectional view taken along the lines 6-6 in FIG. 2showing a preferred embodiment of the new and improveddetector-positioning means of the present invention.

Turning now to FIG. 1, a schematic plan view is shown ofthickness-measuring apparatus 10 arranged in accordance with the presentinvention and operatively mounted within a vehicle 11. To illustrate atypical situation in which the new and improved apparatus 10 can beadvantageously used, the thickness-measuring apparatus is depicted asbeing axially aligned with other pipe-inspection apparatus 12 such asthe flaw-inspection apparatus disclosed in the Tompkins US. Pat. No. RE26,537. As is typical, the thickness-measuring apparatus 10 includespipe-translating means, such as a selectively-powered conveyor 13 (whichmay be the conveyor shown in U.S. Pat. No. 3,565,310) mounted within thevehicle 11 and a pair of portable conveyors l4 and (such as thosedisclosed in U.S. Pat. No. 3,250,404) arranged at the opposite ends ofthe vehicle, for selectively moving pipe sections, as at 16, back andforth through the vehicle along a generallyhorizontal inspection axis17.

Reference should be made, of course, to the aforementioned Tompkinspatent for elaboration of the details of the flaw-inspection apparatus12 and the particulars of its operation. However, the generalarrangement of the flaw-inspection apparatus 12 and a typical inspectionoperation therewith should be understood to better appreciate itscooperation with the new and improved apparatus 10. In general,therefore, the flaw-inspection apparatus 12 is arranged to firstprogressively induce a longitudinally-oriented magnetic flux in ahorizontal pipe, as at 16, being advanced axially in a first directionalong the conveyor 13 so that transversel-y-oriented flaws in the pipecan be concurrently detected. Residual magnetism remaining in the pipe16 is at least partially reduced by progressively subjecting theadvancing pipe to a demagnetizing flux after it has been inspected fortransversely-oriented flaws. When the pipe 16 is also to be inspectedfor longitudinallyoriented flaws, the pipe is moved onto the conveyor 14and, after being halted, subjected to a circumferentially-orientedmagnetic field. Thereafter, as the pipe 16 is returned in the oppositedirection along the inspection axis 17, it is progressively inspectedfor longitudinally-oriented flaws. On the other hand, when this latterinspection is not performed, the pipe 16 is merely returned back throughthe vehicle 11 to the conveyor 15. In either situation, however, it ispreferred that the new and improved thickness-measuring apparatus 10 bearranged for operation upon the return movement of the pipe 16 whetheror not the latter flaw inspection is conducted.

To perform these inspections for transverse flaws, the inspectionapparatus 12 preferably includes an annular coil 18 having spacedsections concentrically arranged around the inspection axis 17 with aplurality of flux-detecting heads 19 arranged therebetween. A secondannular coil 20 is also concentrically arranged around the inspectionaxis 17 to the rear of the flux-inducing coil 18 and connected to asuitable AC or pulsating DC source (not shown) for progressivelydemagnetizing the pipe 16 as it leaves the flux-inducing coil.

The flaw-inspection apparatus 12 further includes anelectrically-conductive, cantilevered elongated probe or lance 21 thatis supported at its remote end and maintained insubstantially-coincidental alignment along the inspection axis 17. Whenthe pipe 16 is to be inspected for longitudinal flaws, it is advancedonto the lance 21 and halted when the lance has passed completelythrough the pipe and its free end projects out of the rearward end ofthe pipe. To subject the pipe 16 to a circumferentially-orientedmagnetic field, a DC source 22 is connected between the remote supportedend of the lance 21 and one or more laterally-movable electricalcontacts 23 that are selectively engageable with the free end of thelance. Thereafter, as the pipe 16 is being returned, a plurality offlux-detecting heads 24 are selectively moved into contact with andcoaxially rotated about the moving pipe for detectinggenerally-longitudinal flaws therein. As previously mentioned, it ispreferred to operate the new and improved thickness-measuring apparatus10 as the pipe 16 is withdrawn from over the lance 21 whether or not thepipe is to be inspected for longitudinal flaws.

In general, as depicted in FIG. 1, the preferred embodiment ofthickness-measuring apparatus 10 incorporating the principles of thepresent invention is comprised of radiation-detecting means including aradiation detector 25 operatively positioned along the axis 17 andradiation means 26 mounted on a body 27 adapted for rotation about theinspection axis and cooperatively arranged with the new and improvedradiation-controlling means 28 of the present invention for directingone or more inwardly-directed beams of radiation through the wall of thepipe 16 for interception by the radiation detector. As will subsequentlybe explained, the radiation-controlling means 28 are cooperativelyarranged with new and improved circuitry 29 and detector-positioningmeans 30 of the present invention for successively checking the accuracyof the detector 25 before each inspection operation.

In a copending application filed simultaneously herewith by the presentinventor Ser. No. 22,932 it is pointed out that the extreme narrownessof the single invention of the present inventor is best suited wheretubular members being inspected are retained as nearly as possible incoincidental alignment with the inspection axis of the apparatus toassure maximum accuracy. In view of these two limiting factors oftheseprior units, therefore, the inspection of elongated tubular memberswhich are slightly bent or the inspection of groups of such members ofwidely-varying diameters require special operating and handlingtechniques which correspondingly reduce the efficiency of the inspectionoperation. Accordingly, although the radiation-controlling means 28, thecircuitry 29, and the detectorpositioning means 30 are equally suitedfor these prior units, the new and improved apparatus and methods of thepresent invention will be described herein in conjunction with the newand improved radiation-emitting means 26 as disclosed and claimed. inthe aforementioned application filed simultaneously herewith.

As illustrated in FIG. 2, therefore, the radiation detector 25 iscomprised of a typical radioactivity detector, such as an ionizationchamber or a scintillation detector, which is mounted in asuitable'enclosed protective housing 31 that is carried on the free endof the elongated probe 21. To adapt the detector 25 for movementrelative to the lower internal wall of the pipe 16 as it is axiallyadvanced or returned along the inspection axis 17, the protectivehousing 31 includes a central tubular portion 32 of nylon, or the like,that will not significantly attenuate incident radiation. In theembodiment illustrated in FIG. 2, a plurality of removable centralizingmembers, as at 33 and 34, are spaced circumferentially about the endportions of the detector housing 31 for retaining the detector 25 ingeneral coincidental alignment with the inspection axis 17 As a matterof convenience, the centralizers 33 and 34 are adapted to be readilyexchanged with other members (not shown) of greater or lesser heights sothat the new and improved inspection apparatus will be effective forinspecting a wide range of sizes of tubular members. As will besubsequently explained, by arranging the radiation means 26 to producediscrete beams of radiation that are each of a reduced transverse widthsomewhat less than that of the effective portion of the detector 25 anddistributing these beams at predetermined intervals across the plane ofrotation, the radiation detector will produce a uniform output signaleven when it is eccentrically disposed in relation to the inspectionaxis 17.

Accordingly, in the preferred embodiment of the thickness-measuringapparatus 10 shown in FIG. 2, the radiation-detector 25 is mounted onthe free end of the lance 21 and coaxially positioned within therotating body 27 which includes a horizontal, generally-tubular member35 having one end portion rotatablyjournalled within an enlarged,annular stationary housing 36 and adapted for high-speed rotationaround. the longitudinal inspection axis 17. Theradiation means 26 areeccentrically located between two longitudinally-spaced annular platesor flanges 37 and 38 secured to the unsupported or other end portion ofthe rotatable member 35. To dynamically balance the rotating body 27, atarget 39 of sufficient mass is mounted between thespaced flanges 37 and38 diametrically opposite of the radiation means 26.

As best seen in FIG. 2, the rotating body 27 is concentrically arrangedabout the horizontal inspection axis 17 and journalled within thehousing 36 by a pair of longitudinally-spaced bearings 40 and 41carrying the supported end portion of the tubular member 35. In onemanner of driving the rotating body 27 at high speeds about itsrotational axis 17, the supported end of the tubular member is extendedbeyond the outboard bearing and coupled to driving means, such as amotor 42 mounted outside of the housing 36, by a suitable powertransmission such as a typical chain or belt 43 operativelyinterconnecting a pulley 44 mounted on the tubular member and a pulley45 mounted on the shaft of the motor.

Turning now to FIG. 3,.the radiation means 26 include an array of threeisotropic radiation sources 46-48 (such as Cobalt 60, Cesium 137, orother acceptable sources of gamma radiation) which are respectivelyencased in typical source cups, as at 49, each having an opening in itslower end. The encapsulated radiation sources 46-48 are respectivelydisposed within one of three chambers, as at 50, formed side-byside inthe upper portion of a block 51 of a suitable radiation-attenuating orshielding material. Tofully eri close the sources 46-48, a removableclosure member, as at 52, is fitted into the open end of each of thesource chambers and a suitable cover plate 53 is secured to theshielding block 51 over each of the closure members.

The radiation means 26 further include particularlyarrangedradiation-focusing means 54 adapted for cooperation with theradiation-controlling means 28 of the present invention which includeselectively-operable shutter means 56 disposed between the focusingmeans and the radioactive. sources 46-48. As best seen in FIG. 3, thefocusing means 54 are comprised of a second block 57 formed of steel,tungsten, lead or some other suitable radiation-attenuating or shieldingmaterial that is mounted between the annular flanges 37 and 38 andspaced radially inwardly from the shielding block 51 and diametricallyopposite from the target shield 39 (FIG. 2). The shutter means 56 arecomprised of a third block 58 of radiation-shielding material mountedbetween the shielding block 51 and the focusing block 57 and havingthree generally-parallel radiation passages, as at 59, which arerespectively aligned with three corresponding radiation passages, as at60 and 61, respectively formed in the first and second blocks. As willsubsequently be explained in greater detail and of paramountsignificance to the present invention, it will be seen that the shuttermeans 56 are uniquely arranged for selectively controlling the passageof radiation from the sources 46-48 to the detector 25.

It will be noted from FIG. 3 that the radioactive sources 46-48 areuniquely arranged so that separate, generally-parallel beams ofradiation 62-64 are directed along a selected transverse planeintersecting the inspection axis 17. In particular, the radiation means26 are arranged so that two of the three radiation beams 62 and 64 arerespectively directed on opposite sides of the axis 17 and the thirdbeam of radiation 63 will intersect the inspection axis. Accordingly,when the detector 25 is in position and coincidentally aligned with theinspection axis 17, the radiation beam 63 from the central radioactivesource 47 will be directly impinged on the detector and the exterior orflanking beams of radiation 62 and 64 will substantially uniformlystraddle the detector. On the other hand, as schematically depicted bythe dashed circles 65 and 66, should the detector 25 be shiftedlaterally to either side of the inspection axis 17, the active portionof the detector will progressively receive more radiation from one orthe other of the two flanking beams 62 (or 64) and correspondinglyreceive a lesser amount of radiation from the central beam 63.

Accordingly, as explained in greater detail in the copending applicationSer. No. 22,932, by selecting a given energy or intensity for thecentral radioactive source 47, so long as the detector 25 remainscoincidentally aligned with the inspection axis 17 the maximum intensityof the central radioactive source will be received thereby so as toproduce the maximum output. On the other hand, lateral movement of thedetector 25 to either one side or the other of the inspection axis 17will progressively diminish the radiation intensity being received fromthe central source 47 by the detector and produce acorrespondingly-reduced output signal. The same results will, of course,be obtained for each of the two flanking sources 46 and 48.

Accordingly, by selecting the sources 46 and 48 to have equal but lesserstrengths than the central source 47 and cooperatively arranging the twoflanking radioactive sources in the manner depicted in FIG. 3, as thedetector 25 shifts to one side or the other of the inspection axis 17,the detector will be irradiated by a combination of one of the twoflanking radiation beams, for example the left-hand beam 62, as well asthe central radiation beam 63. Thus, as the detector 25 moves further tothe left, the progressively-increasing signal produced by the weakerradioactive source 46 will be added to the progressively-diminishingsignal produced by the central radioactive source 47 so as to produce acombined output that is substantially constant. The same response will,of course, be obtained whenever the detector 25 shifts to the right-handside of the inspection axis 17 except that the right-hand radioactivesource 48 will produce a progressivelygreater output signal as theoutput signal contributed solely by the central radioactive source 47progressively diminishes. It will, of course, be appreciated that thestrengths of the two flanking sources 46 and 48 are cooperativelyselected in accordance with their lateral spacing from the centralsource 47 to obtain the additional intensity to make the combined outputsubstantially constant across the range of lateral movements of thedetector 25.

It will be appreciated, therefore, that the radiation means 26 willproduce a substantially-uniform output signal for a given thickness ofmetal between the radiation sources 46-48 and the detector 25 so as toat least minimize the effects which would otherwise be caused by eventhe slightest lateral shifting of the detector within the pipe 16. Itshould also be noted that even though the detector 25 may bounceupwardly and downwardly as the pipe 16 is being moved thereover,

the radiation means 26 will also provide substantiallyuniform signalsover an acceptable range of vertical movement of the detector inasmuchas the radiation beams 62-64 are well co'llimated and the sides of eachbeam'is relatively parallel'so that the flux density of each beam willbe substantially equal at different verti- 1 cal positions within therange of vertical movement of the detector. Thus, the vertical movementsof the detector 25 are usually within a range where the axes of theradiation beams 62-64 can be perfectly parallel and still maintain asubstantially-equal flux density within this range. It has been found,however, that by arranging the outer radiation passages 59 and 61 toconverge the flanking beams 62 and 64 slightly inwardly a few degrees,the outer radiation patterns will be moved slightly inwardly toward thecentral radiation pattern to produce a more-uniform flux density over agreater range of vertical movements of the detector 25 without reducingits range of lateral movements.

Accordingly, the radiation-controlling means 28 of the present inventionare operatively arranged for selectively attenuating the radiation beams62-64 at all times that a pipe, as at 16, is not positioned over thedetector 25. Thus, by reducing the intensity of radiation intercepted bythe detector 25 to at least a reduced level that will not create theaforementioned unstability or drifting of the detector, the new andimproved thickness-measuring apparatus 10 can be operated at efficientinspection rates without compromising the accuracy of the resultingmeasurements.

Referring again to FIGS. 2 and 3, it will be noted that the shuttermeans 56 include three elongated rods, as at 67, that are respectivelyarranged for sliding movement within complementary passages 68 formed inthe block 58 and respectively intersecting the radiation passages 59therein. In the preferred embodiment of the shutter means 56, theseintersecting passages 68 are parallel to the inspection axis 17 and theelongated rods 67 are of sufficient length that they will projectoutwardly from the forward and rearward faces of the flanges 37 and 38.

As best seen in FIGS. 2 and 3, each of these bars 67 are provided with afirst portion having a transverse port, as at 69, formed therein of asimilar or identical cross section as the radiation passages 59 andthrough which radiation may readily pass when these transverse openingsare in registration with the radiation passages 59. Of significance tothe present invention, it will be noted that a second portion, as at 70,of each of the bars 67 is formed to have a thickness of a selected andpredetermined magnitude so that upon movement of the bars to positionthese reduced portions in alignment with the radiation passages 59, theradiation intercepted by the radiation detector 25 will be reduced toproduce a selected count rate at the detector.

In the preferred embodiment of the new and improvedradiation-controlling means 28 of the present invention, the shuttermeans 56 are further arranged for selectively moving the shutter rods 67to bring their respective openings 69 into registration with theradiation passages 59 just as the leading end of the pipe 16 approachesthe detector 25 and then repositioning the rods to bring theirrespective obturating portion 70 back into the radiation passages 59 asthe trailing end of the moving pipe passes over the detector. It will be9 appreciated, therefore, that these altemately-directed movements ofthe shutter bars 67 between their respective positions will assure thatthe detector 25 will be protected from exposure to excessive radiationintensities that could otherwise create the aforementioned problems withunstability or drifting of the detector.

In the preferred manner of accomplishing these alternately-directedmovements of the shutter bars 67 and as disclosed and claimed in acopending application Ser. No. 22,933 filed simultaneously herewith,rounded knobs, as at 71 and 72, are mounted on the outer ends of each ofthe rods. Since the rods 67 will follow approximately the same circularpath upon rotation of the rotating body 27, straps, as at 73 and 74(FIG. 1), of a relatively-flexible material are respectively secured tothe forward and rearward portions of the housing 36 and operativelyarranged for pivotal movement from first positions away from the housingto second positions immediately adjacent thereto which respectivelyintercept the paths of rotation of the forward and rearward knobs 71 and72. Selectivelyoperated solenoid actuators 75 and 76 are arrangedadjacent to the straps 73 and 74, respectively, and so located that,upon energization of the first actuator 75, the strap 73 will be movedinto the rotational path of the knobs 71 and will accordingly shift theshutter rods 67 to the position illustrated in FIG. 2 before therotating body 27 completes a full revolution. Conversely, by energizingthe second actuator 76, the shutter rods 67 will be quickly shifted inthe reverse direction to their alternate position for opening theradiation passages 59. In the preferred embodiment of thethickness-measuring apparatus 10, the selective operation of thesolenoid actuators 75 and 76 is accomplished by arranging typical limitswitches, as at 77 and 78 in FIG. 1, for contact by the pipe 16 as itpasses along the conveyor 13 to shift the shutter rods 67 back and forthin proper coordination with the operation of the thickness-measuringapparatus.

Turning now to FIG. 4, the new and improved circuitry 29 of the presentinvention is depicted. In general, as will be subsequently described byreference to FIGS. 5A-5D, the circuitry 29 is uniquely arranged so thateach time the shutter rods 67 are in their radiation-blocking positions,a calibration measurement is made of the thickness of the obturatingportions 70 of the rods. Then, as a pipe, as at 16, is being inspected,the resulting thickness measurements being obtained are compared withthe previously-obtained calibration measurement for determining theaccuracy of these thickness measurements.

To convert the output signal of the radiation detector 25 to ameaningful record, the output of the detector is coupled by way ofsuitable conductors 79 and 80 and an amplifier 81 to an indicator, suchas a recorder 82, that is appropriately arranged for progressivelyproviding a continuous first indication representative of the wallthickness of a tubular member passing through the inspection apparatus10. As an additional feature, the circuitry 29 also includesatime-averaging circuit 83 appropriately tuned to average the output ofthe detector 25 for each revolution ofthe sources 46-48 to provide asecond indication, ason a typical recorder 84, representative of thetransverse cross-sectional metal area through that portion of thetubular member 10 scanned in that revolution. In this manner, by drivingthe recorders 82 and 84 at speeds related to the axial speed of the pipe16 past the apparatus 10, continuous meaningful records will be obtainedof the actual metal thicknesses along the generally-helical inspectionpath around the pipe as well as of successive transverse cross-sectionalmetal areas along; the length of the pipe.

The circuitry 29 further includes alarm indicators, as at 85 and 86,coupled to the recorders 82 and 84 and adapted for warning the operatorof the apparatus 10 that the respective thickness and area measurementsare less than some selected minimum value.

To provide the aforementioned calibration measurements, the circuitry 29further includes a normallyopen relay 87 which is appropriatelyconnected to the solenoid actuator 76 and adapted to be closed when theshutter rods 67 are in their radiation-blocking positions. In thismanner, when the radiation passages 59 are closed, the output of thedetector 25 will be temporarily coupled by way of an adder 88, afollower 89, and an inverting adder 90 to the amplifier 81 to produce aninput signal at the recorder 82 that corresponds to the known thicknessof the obturating portions 70 of the shutter bars 67. Aselectively-adjustable reference signal, such as provided by aconstant-voltage source 91 and a potentiometer 92, is coupled to theother input of the adder 88 for accurately resetting the recorder 82before the first pipe that is to be inspected is passed through thethickness-measuring apparatus 10. Once this reference signal iscorrectly set, the potentiometer 92 is not changed until such time thatthe thickness-measuring apparatus 10 is again recalibrated.

For reasons that will subsequently be explained, the adder 88 is asignal-inverting adder so that the combination of the detector outputsignal and the reference signal will be inverted by the adder to providea calibration signal. The calibrated output signal from the invertingadder 88 is stored by a capacitor 93, and by employing thehigh-impedance follower 89, will remain as a fixed input to the adder 90after the relay 87 is opened. It will be appreciated, therefore, thatwhen the relay 87 is closed and the reference signal is applied to thefirst inverting adder, the inversion of the signals by the adder 88 willproduce an output signal from the second adder 90 that equals only thereference signal. On the other hand, the signal initially stored by thecapacitor 93 will be the inverted summation of the reference signal andthe output signal of the detector 25 at the time the radiation passages59 are blocked.

Accordingly, as best seen in FIG. 5A, once the reference signal (e hasbeen properly set to obtain the correct reading at the recorder 82corresponding to the thickness of the obturating portions 70, thepotentiometer 92 is left alone. Those skilled in the art will, ofcourse, appreciate that since the scattering of the radiation beams62-64 will be dependent upon the diameter of the tubular member beinginspected, an empiricallydetermined compensation factor must be includedwith the reference signal (e,,) which will be established by the settingof the potentiometer 92. Thus, for each diameter of pipe, a differentempirical factor will be determined for arriving at the magnitude of thereference signal, e Then, as the first pipe, as at 16, is being movedinto the inspection apparatus 10, the relay 87 will open and leave thecapacitor 93 charged with the summed signal, e =e As shown in FIG. B, asthe thickness measurements are being obtained, it will be appreciatedthat the output signal (e, e e,) of the adder 90 will be equal to thealgebraic summan'on of the reference signal (e,,) and the difference inthe output signal of the detector 25 at that moment (e and the detectoroutput signal (e,) at the time the recorder 82 was calibrated. Thus, thesignal (e,, e, e,) that is recorded by the recorder 82 will, in effect,be the differences between the varying wall thicknesses of the pipe 16and the known thicknesses of the obturating portions 70 of the shutterbars 67. These readings can, of course, be presented on the recorder 82either as a true thickness measurement or as the difference between thisknown thickness and the thickness then being measured.

Once the first pipe has been inspected, the shutter bars 67 will, ofcourse, be reclosed and, as shown in FIG. 5C, the relay will still beclosed when the next pipe is ready for inspection. AT this time, ifthere has been drifting of the detector 25, the calibration signal (-e,e,,) that is then stored on the capacitor 93 will be the invertedalgebraic summation of the unchanged reference signal (e,,) and theoutput signal (e of the detector which will be then produced as a resultof any drifting. It will berecalled that the potentiometer 92 is notchanged. Thus, with the relay 87 being reclosed, the output of the adder90 will again be momentarily equal to only the original unchangedreference signal (e,,) which will indicate that the circuitry 29 isstill properly calibrated.

Once the next pipe is moved through the thicknessmeasuring apparatus andthe relay 87 is reopened as shown in FIG. 5D, the resulting outputsignal (e,, e e,) from the adder 90 will again be equal to the algebraicsummation of the reference signal (e,,) and the difference in the outputsignal of the detector at that moment (e,) and the detector outputsignal (e;,) at the time the second calibrating signal (-1,, e;,) wasstored on the capacitor 93. I-Iereagain, the resulting signal (e e erecorded by the recorder 82 will be representative of the differences inthe thicknesses of the pipe being inspected and the known thickness ofthe obturating portions 70 of the shutter bars 67. It will beappreciated, therefore, that any drifting of the detector betweensuccessive inspection operations will be completely compensated since anew calibration signal is stored on the capacitor 93 just before eachinspection operation. Drifting errors during the actual inspectionoperation will, of course, be only negligible at worse.

It will be appreciated that a more-precise calibration signal can bestored in the capacitor 93 if the detector 25 is in a known position inrelation to the radiation sources 46-48. Accordingly, thedetector-positioning means of the present invention are provided fortemporarily fixing the detector 25 in a selected position as thecalibration measurements are being obtained.

Accordingly, in the preferred manner of accomplishing this, first andsecond selectively-operable clamping devices 94 and 95 (FIGS. 1 and 2)are arranged at opposite ends of the tubular member and cooperativelyarranged to secure the detector 25 in coincidental alignment with theinspection axis 17 as a calibration measurement is being obtained. Ingeneral, each of the clamping devices 94 and 95 is comprised of anopposed pair of clamps, as at 96 and 97 (FIG. 6), which are respectivelydisposed above and below the conveyor 13 and operatively carried forvertical movement on suitable guides or uprights 98 and 99 stationed onopposite sides of the conveyor. Suitable devices, such assolenoid-actuators or hydraulic piston actuators as at 100 and 101, areoperatively coupled to the clamps 96 and 97, respectively, and suitablyarranged for moving the opposed clamps in unison into clampingengagement on the respective end portions of the detector housing 31 forcoaxially positioning the detector 25 therein when a calibrationmeasurement is to be made. Once the calibration measurement iscompleted, the actuators 100 and 101 are reversed to return the clamps96 and 97 to their normal positions so that the pipe 16 can freely passthrough the clamping devices 94 and 95.

To employ the thickness-measuring apparatus 10 for practicing the newand improved methods of the present invention, a pipe, as at 16, isplaced on the conveyor l5 and advanced (to the left as viewed in FIG. 1)along the conveyor 13 and over the elongated lance 21 at the oppositeend of the vehicle 11. It will, of course, be appreciated that if theflaw-inspection apparatus 12 is being operated, the first inspection tobe made with this apparatus will be performed as the pipe 16 passesalong the conveyor 13.

In any event, once the pipe 16 is on the conveyor 14 and has passed thedetector 25, the pipe is momentarily halted and the clamping devices 94and 95 are actuated. At this point, the shutter bars 67 will be in theirradiation-blocking positions to reduce the intensity of the radiationintercepted by the detector 25. Thus, since the obturating portions ofthe shutter bars 67 will always provide a constant output signal which,since the relay 87 (FIG. 4) is then closed, will be stored in thecapacitor 93.

Once this reference signal is obtained, the clamping devices 94 and 95are operated to move their respective clamps 96 and 97 out of the pathof the pipe 16 and the pipe is returned back along the conveyor 13through the rotating body 27. As previously described, as the leadingend of the pipe 16 nears the thickness measuring apparatus 10, theactuator will be operated for shifting the shutter bars 67 to bringtheir ports 69 into alignment with the radiation passages 59 before therotating body 27 completes a full revolution.

As the pipe 16 passes through the rotating body 27, one wall of the pipewill be interposed between the radiation means 26 and the detector 25 toproduce a varying signal representative of the thickness of eachincremental portion of the pipe wall being progressively scanned by theradiation beams 62-64. This varying signal will be combined by the adderwith the previously-obtained calibration signal that is stored in thecapacitor 93 to provide an output signal from the amplifier 81 that isrepresentative of the difierences between the known thickness of theobturating portions 70 of the shutter bars 67 and the wall thicknessesof the pipe 16. Once the trailing end of the pipe 16 clears the detector25, the actuator 76 is operated to reposition the obturating portions 70of the shutter bars 67 into alignment with the radiation passages 59 foragain reducing the intensity of radiation to an acceptable level. Thethicknessmeasuring apparatus is then in readiness for accepting anotherpipe once the pipe 16 is removed from the conveyor 15.

It will be appreciated, therefore, that the present invention hasprovided new and improved radiation apparatus and methods for accuratelyand quickly measuring the wall thickness of elongated tubular members.By arranging the new and improved radiationcontrolling means forselectively blocking one or more narrowly-focused beams of radiationwhich are directed toward the radiation detector, a calibration signalwill be obtained. Then, as a tubular member is advanced along theinspection axis and over the detector, the radiation-controlling meanswill function for successively obtaining thickness measurements of thetubular member passing along the axis. By successively comparing thesesignals with the calibrating signals respectively obtained before eachinspection operation, drifting of the detector will be effectivelycompensated and more accurate measurements obtained. Moreover, byselectively positioning the detector as each calibration signal isobtained, it will be assured that the detector is correctly calibrated.

While particular embodiments of the present invention have been shownand described, it isapparent that changes and modifications may be madewithout departing from this invention in its broader aspects; and,therefore, the aim in the appended claims is to cover all such changesand modifications as fall within the true spirit and scope of thisinvention.

What is claimed is:

1. A method for measuring the thickness of different wall portions of anelongated tubular member comprising the steps of: positioning a standardmember of a known thickness in a beam of radiation produced byradiation-emitting means and directed toward radiation-detecting meansfor obtaining a calibrating signal representative of the attenuation ofsaid beam of radiation by said standard member; storing said calibratingsignal; inserting one of said radiation means into an elongated tubularmember for interposing the wall of said tubular member between said oneradiation means and the other of said radiation means; moving saidtubular member in relation to said radiation means for obtainingsuccessive signals respectively representative of the attenuation ofsaid beam of radiation produced by different wall portions of saidtubular member interposed between said radiation means; and combiningsaid stored calibrating signal with said successive signals forproducing a plurality of signals respectively representative of thedifferences between said known thickness and the respective thicknessesof said different wall portions.

2. The method of claim 1 wherein said one radiation means is saidradiation-detecting means.

3. The method of claim 1 wherein said tubular member is moved axially sothat said different wall portions thereof are at longitudinally-spacedpositions along the length of said tubular member.

4. The method of claim 3 wherein said one radiation means is saidradiation-detecting means and said radiation-detecting means include aradiation detector adapted to be inserted into said tubular member forintercepting said beam of radiation upon rotation of saidradiation-emitting means about said tubular member;

and further including the step of rotating said radiationernitting meansabout said tubular member as said tubular member is moved axially sothat said successive signals are respectively representative of theattenuation by different wall portions of said tubular member disposedalong a generally-helical path therealong.

5. Apparatus adapted for measuring the thickness of a test membercomprising: radiation-emitting means adapted for directing a beam ofradiation along a selected axis; radiation-detecting means including aradiation detector positioned on said axis for receiving said beam ofradiation and adapted for producing signals representative of theintensity of radiation received by said radiation detector; controllingmeans including a member having a radiation-attenuating portion of knownthickness adapted for movement into and out of said beam of radiationbetween said radia tion-emitting means and said radiation detector; andsignal-comparing means operatively coupled to said radiation detectorand adapted for comparing first signals produced thereby when only saidradiation-attenuating portion is intersected by said beam of radiationwith second signals produced by said detector when only a test member ofan unknown thickness is intersected by said beam of radiation, saidsignal-comparing means including means coupled to said radiationdetector and adapted for storing said first signals as said firstsignals are being produced, and means coupled to said radiation detectorand to said signal-storing means and adapted for combining said firstsignals with said second signals as said second signals are beingproduced to produce third signals representative of the differencebetween said known thickness and the thickness of a test membersubsequently interposed between said radiation detector and saidradiationemitting means.

6. The apparatus of claim 5 further including: clamping meansselectively operable for releasably securing said radiation detector ina known position in relation to said radiation-emitting means when saidfirst signals are being produced.

7. The apparatus of claim 5 further including: means adapted for movinga test member relative to said radiation detector and saidradiatiomemitting means for obtaining a series of said second signalsrespectively representative of the radiation attenuation produced bysuccessive portions of such a test member for comparison with said firstsignals.

8. The apparatus of claim 7 wherein said moving means are adapted formoving a test member into and out of positions between said radiationdetector and said radiation-emitting means to obtain said secondsignals.

9. The apparatus of claim 7 wherein said moving means are adapted formoving one of said radiation means in relation to the other of saidradiation means and a test member interposed therebetween to obtain saidsecond signals.

10. The apparatus of claim 9 wherein said one radiation means is saidradiation-emitting means.

11. Apparatus adapted for measuring the wall thickness of an elongatedtubular member comprising: radiationdetecting means including aradiation detector adapted for insertion into a tubular member toreceive radiation directed laterally therethrough; radiation-emittingmeans spaced from said radiation detector and operatively arranged fordirecting a beam of radiation theretoward; radiation-controlling meansincluding a movable member having a first portion of a known thicknessadapted for interposition between said radiation-emitting means and saidradiation detector to attenuate said beam of radiation to a selectedintensity and a second portion having a radiation passage thereinadapted for passing said beam of radiation, and means adapted forselectively shifting said movable member between first and secondpositions to respectively position said first and second portions insaid beam of radiation; first signal means coupled to said radiationdetector and operable when only said first portion of said movablemember is positioned in said beam of radiation for producing a firstsignal representative of said known thickness and storing said firstsignal as said first signal is being produced; second signal meanscoupled to said radiation detector and operable only when said radiationpassage is positioned in said beam of radiation and said radiationdetector is inserted into a tubular member for producing a second signalrepresentative of the wall thickness thereof; signal-comparing meansoperatively coupled to said first and second signal means and adaptedfor combining said stored first signal and said second signal as saidsecond signal is being produced to produce a third signal representativeof the difference between said known thickness and the wall thickness ofa tubular member disposed over said radiation detector; and meansoperable only upon insertion of said radiation detector into a tubularmember for shifting said movable member from its said first position toits said second position. 1

12. The apparatus of claim 11 further including: means adapted foraxially moving a tubular member back and forth in relation to saidradiation detector to obtain a series of said second signalsrespectively representative of the wall thicknesses of successiveportions of such a tubular member so that said signal-comparing meanswill combine said first and second signals to produce said third signalsfor measuring the differences between said known thickness and the wallthicknesses of successive portions of a tubular member moving over saidradiation detector.

13. The apparatus of claim 12 wherein said radiation detector isresponsive to radiation imposed thereon from any lateral directionthereabout and further including: means coupled to saidradiation-emitting means and operatively arranged and adapted forrotating said radiation-emitting means about said radiation detector fordirecting a lateral beam of radiation theretoward whenever a tubularmember is disposed over said radiation detector so that said thirdsignals will be respectively representative of the differences betweensaid known thickness and the wall thickness of successivehelically-distributed portions of a tubular member moving over saidradiation detector.

14. The apparatus of claim 13 further including: clamping meansselectively operable for releasably securing said radiation detector ina known position in relation to said radiation-emitting means when saidfirst signals are being produced.

1. A method for measuring the thickness of different wall portions of anelongated tubular member comprising the steps of: positioning a standardmember of a known thickness in a beam of radiation produced byradiation-emitting means and directed toward radiation-detecting meansfor obtaining a calibrating signal representative of the attenuation ofsaid beam of radiation by said standard member; storing said calibratingsignal; inserting one of said radiation means into an elongated tubularmember for interposing the wall of said tubular member between said oneradiation means and the other of said radiation means; moving saidtubular member in relation to said radiation means for obtainingsuccessive signals respectively representative of the attenuation ofsaid beam of radiation produced by different wall portions of saidtubular member interposed between said radiation means; and combiningsaid stored calibrating signal with said successive signals forproducing a plurality of signals respectively representative of thedifferences between said known thickness and the respective thicknessesof said different wall portions.
 2. The method of claim 1 wherein saidone radiation means is said radiation-detecting means.
 3. The method ofclaim 1 wherein said tubular member is moved axially so that saiddifferent wall portions thereof are at longitudinally-spaced positionsalong the length of said tubular member.
 4. The method of claim 3wherein said one radiation means is said radiation-detecting means andsaid radiation-detecting means include a radiation detector adapted tobe inserted into said tubular member for intercepting said beam ofradiation upon rotation of said radiation-emitting means about saidtubular member; and further including the step of rotating saidradiation-emitting means about said tubular member as said tubularmember is moved axially so that said successive signals are respectivelyrepresentative of the attenuation by different wall portions of saidtubular member disposed along a generally-helical path therealong. 5.Apparatus adapted for measuring the thickness of a test membercomprising: radiation-emitting means adapted for directing a beam ofradiation along a selected axis; radiation-detecting means including aradiation detector positioned on said axis for receiving said beam ofradiation and adapted for producing signals representative of theintensity of radiation received by said radiation detector; controllingmeans including a member having a radiation-attenuating portion of knownthickness adapted for movement into and out of said beam of radiationbetween said radiation-emitting means and said radiation detector; andsignal-comparing means operatively coupled to said radiation detectorand adapted for comparing first signals produced thereby when only saidradiation-attenuating portion is intersected by said beam of radiationwith second signals produced by said dEtector when only a test member ofan unknown thickness is intersected by said beam of radiation, saidsignal-comparing means including means coupled to said radiationdetector and adapted for storing said first signals as said firstsignals are being produced, and means coupled to said radiation detectorand to said signal-storing means and adapted for combining said firstsignals with said second signals as said second signals are beingproduced to produce third signals representative of the differencebetween said known thickness and the thickness of a test membersubsequently interposed between said radiation detector and saidradiation-emitting means.
 6. The apparatus of claim 5 further including:clamping means selectively operable for releasably securing saidradiation detector in a known position in relation to saidradiation-emitting means when said first signals are being produced. 7.The apparatus of claim 5 further including: means adapted for moving atest member relative to said radiation detector and saidradiation-emitting means for obtaining a series of said second signalsrespectively representative of the radiation attenuation produced bysuccessive portions of such a test member for comparison with said firstsignals.
 8. The apparatus of claim 7 wherein said moving means areadapted for moving a test member into and out of positions between saidradiation detector and said radiation-emitting means to obtain saidsecond signals.
 9. The apparatus of claim 7 wherein said moving meansare adapted for moving one of said radiation means in relation to theother of said radiation means and a test member interposed therebetweento obtain said second signals.
 10. The apparatus of claim 9 wherein saidone radiation means is said radiation-emitting means.
 11. Apparatusadapted for measuring the wall thickness of an elongated tubular membercomprising: radiation-detecting means including a radiation detectoradapted for insertion into a tubular member to receive radiationdirected laterally therethrough; radiation-emitting means spaced fromsaid radiation detector and operatively arranged for directing a beam ofradiation theretoward; radiation-controlling means including a movablemember having a first portion of a known thickness adapted forinterposition between said radiation-emitting means and said radiationdetector to attenuate said beam of radiation to a selected intensity anda second portion having a radiation passage therein adapted for passingsaid beam of radiation, and means adapted for selectively shifting saidmovable member between first and second positions to respectivelyposition said first and second portions in said beam of radiation; firstsignal means coupled to said radiation detector and operable when onlysaid first portion of said movable member is positioned in said beam ofradiation for producing a first signal representative of said knownthickness and storing said first signal as said first signal is beingproduced; second signal means coupled to said radiation detector andoperable only when said radiation passage is positioned in said beam ofradiation and said radiation detector is inserted into a tubular memberfor producing a second signal representative of the wall thicknessthereof; signal-comparing means operatively coupled to said first andsecond signal means and adapted for combining said stored first signaland said second signal as said second signal is being produced toproduce a third signal representative of the difference between saidknown thickness and the wall thickness of a tubular member disposed oversaid radiation detector; and means operable only upon insertion of saidradiation detector into a tubular member for shifting said movablemember from its said first position to its said second position.
 12. Theapparatus of claim 11 further including: means adapted for axiallymoving a tubular member back and forth in relation to said radiationdetector to obtain a series of said second Signals respectivelyrepresentative of the wall thicknesses of successive portions of such atubular member so that said signal-comparing means will combine saidfirst and second signals to produce said third signals for measuring thedifferences between said known thickness and the wall thicknesses ofsuccessive portions of a tubular member moving over said radiationdetector.
 13. The apparatus of claim 12 wherein said radiation detectoris responsive to radiation imposed thereon from any lateral directionthereabout and further including: means coupled to saidradiation-emitting means and operatively arranged and adapted forrotating said radiation-emitting means about said radiation detector fordirecting a lateral beam of radiation theretoward whenever a tubularmember is disposed over said radiation detector so that said thirdsignals will be respectively representative of the differences betweensaid known thickness and the wall thickness of successivehelically-distributed portions of a tubular member moving over saidradiation detector.
 14. The apparatus of claim 13 further including:clamping means selectively operable for releasably securing saidradiation detector in a known position in relation to saidradiation-emitting means when said first signals are being produced.